Thermally insulated wall structure



1950 M. R. JEPPSON THERMALLY msummn WALL STRUCTURE Filed Jan. 3. 1956 INV EN TOR.

Uniten St 2,961,116 Patented Nov. 22, 1960 hiorris R. Jeppson, Orinda,Radiation Corporation, ration of California Filed Jan. 3, 1956, Ser. No.557,025

'3 Claims. (Cl. 220-9) Calif., assignor to Applied Walnut Creek, Califi,a corpo- The invention relates to methods and means for insulatingstructural elements against the passage of heat therethrough, and moreparticularly to elements employing vacuum as a thermal barrier.

Modern shipping and construction techniques have created a need forlight weight wall structures combining highly eflicient heat insulatingqualities with strength and rigidity. For example, new methods ofshipping frozen foods include super-freezing the foods with liquidnitrogen and shipping them in insulated containers without anyadditional refrigeration en route. The containers utilized in suchmethods of shipping should provide extremely efficient heat insulationfor the superfrozen contents, minimum wall thickness to conserve space,suificient strength to withstand the hazards of shipping, and as light aweight as possible. A wall structure incorporating these characteristicsmay also be valuable in the construction of articles suitable forairborne and shipboard use and especially when very high or lowtemperatures are to be anticipated.

One of the most etficient known methods of insulating a wall structureagainst heat transfer is to construct it with spaced wall members havinga vacuum therebetween in the nature of the well known Dewar flask orvessel. Perhaps the greatest problem in attempting to utilize suchconstruction in any but relatively small containers is the necessity ofproviding comparatively thick and heavy walls strong enough to preventcollapse of the structure when evacuated. Various contrivances have beenproposed for diminishing the required wall thickness, among which aredevices intended to fit within the vacuum space and brace the wallsagainst collapse. Such contrivances have heretofore been foundimpractical in that they do not provide adequate reinforcement, greatlylower the insulation qualities of the structure by providing increasedheat conductivity between the double walls, and also in that they arecomplicated and expensive to manufacture and are relatively heavy inweight.

The main types of heat transfer present in reinforced vacuum wallconstruction are transfer by conduction and by radiation. The presentinvention contemplates a structure incorporating a sturdy andlightweIght reinforcing means which will provide an elfective barrier toheat conduction and radiation in combination with improved evacuationmethods. Use is made of the fact that heat transfer by conductionbetween two bodies in physical contact can be practically eliminated bymaking the contacting areas as small as possible and removingsubstantially all the air or other gases at such areas. Prevention ofheat transfer between the double walls by radiation may be and isefiected by placing insulating material between the walls so that heatradiated from one wall will be intercepted by the insulation, the heatthen having to pass through the insulation, where it will be impeded bythe resistance to thermal conduction of the insulation, and finally bere-radiated from the insulation to the other of the double walls.

Accordingly, a principal object of the present invention is to provide adouble wall evacuated heat insulated structure which is amply strong andsturdy for use in large containers and the like and at the same time islight in weight so as to reduce shipping and handling costs.

Another object of the present invention is to provide a structure of thecharacter described which is simple and easy to construct, incorporatesa minimum number of parts, and is inexpensive to produce.

A further object of the present invention is the provision of a heatinsulating structure of the character described which utilizes a novelreinforcing means affording exceptionally efiicient heat insulatingcharacteristics.

A still further object of the present invention is the provision of adouble wall evacuated heat insulating structure adaptable to a varietyof applications such as containers of various sizes and shapes designedto accommodate difierent types of contents, and applications requiringdiverse forms of heat insulating wall structures.

Another object of the present invention is to provide a method ofeffecting an efiicient heat insulation of a double wall heat insulatingstructure of the nature described.

A further object of the present invention is to provide a method ofeffecting heat insulation in a structure of the character descnbed whichwill afford an effective barrier against heat conduction throughimproved evacuation, the method being cooperative with the physicalcharacteristics of the wall reinforcing means.

Other objects and features of advantage within the scope of theinvention will be apparent from a consideration of the followingdescription and the accompanying drawing, wherein:

Figure l is a perspective view of a heat insulated container havingwalls constructed in accordance with the present invention, portions ofthe walls being broken away and shown in section for clarity ofillustration.

Figure 2 is a side elevational view of a heat insulated contaner havingwalls constructed in accordance with the present invention andparticularly adapted for containing fluids.

Figure 3 is a typical enlarged crosssectional view of a heat insulatedwall structure constructed in accordance with the present invention.

The heat insulating wall construction of the present invention, and asillustrated in the accompanying drawing, includes a pair of rigidmembers 11 and 12 of sheetlike form positioned in spaced relation andjoined at their edges to define an air tight chamber 13, and a core 14of rigid, expanded material mounted in the chamber and formed to providea plurality of points 16 extending into supporting engagement with therigid members 11 and 12, the chamber 13 being evacuated to provideeffective thermal barriers between the members 11 and 12 and the core14. In accordance with the invention, the core 14 is formed of a rigid,expanded insu'ating material which is light in weight and at the sametime sufficiently resistant to compression to reinforce the rigidmembers 11 and 12 against collapsing under surrounding pressures Whenthe compartment 13 is evacuated.

The wall construction of the present invention is adapted for a varietyof applications where a wall-like structure providing an effectivethermal barrier is required, such as insulating areas or entirecompartments of airplanes, land vehicles, ships, submarines and thelike. The rigid wall members 11 and 12 may be planar or curved in formto accommodate the construction desired, with the core 14 formed in likemanner, and the structure divided into one or more air tight chamberswhich may be evacuated in the manner to be described later. The rigidmembers 11 and 12 may be formed of any material suitable for the useintended, it being noted in this connection that relatively weak andfrangible materials of minimum thickness may be used in one of themembers, such as the lining of a container, because of the reinforcingaction ofv the core 14. In this manner, thin walls of collapsible oreven relatively brittle substances such as glass or the like can beused, particularly wherein the materials contacting such walls dictatethe useof corrosive-resistant substances. In such cases, thin,light-weight materials may be used for walls while still maintaining thedesired structural rigidity and strength not otherwise possible withoutsupport by a core member. Figure 3 of the accompanying drawingillustrates a typical section through a wall structure constructed inaccordance with the present invention. Here the wall member 11 isindicated as being of thin sheet metal, while the opposed member 12 isof a thicker gauge. The core 14 is interposed between the wall membersand transmits pressures imposed on the thinner wall 11 to the moresturdy wall 12.

As an important feature of the invention, the core 14 is formed toafford a minimum of contact area with the wall members 11 and 12 inorder to cut down to a minimum the transmission of heat by conductionbetween the wall members and core. This is accomplished by forming thecore with a plurality of points 16 extending therefrom and into contactwith the rigid wall members; a relatively great number of these pointsbeing scattered uniformly over the surface of the core member so as toprovide effective support over the entire area of the rigid members 11and 12. To provide such a plurality of points in a simple and economicalmanner, the core 14 is preferably formed of a foamed material ofunicellular construction as illustrated in Figure 3, in which theupstanding Walls of the cells 17 will afford the points 16 when thematerial is cut to conform to the shape of the members 11 and 12.

In accordance with the method of insulating the wall of the presentinvention, the chamber 13 is evacuated as through tube 18 to removesubstantially all of the gases and/or vapor present at the points 16where they contact the rigid members 11 and 12 so as to provide a moreefficient heat barrier than would be the case if such gases or vaporwere present. While an ordinary high vacuum would be quite effective inthis connection, the efliciency of the heat barrier increases in inverseratio to the amount of gases present and, therefore, it is desired toremove all the surface gases possible. As an important feature of theinvention, the wall structure is heated so as to bake ofr' surfacegases. In carrying out the method, the structure is first assembled tocreate the air tight chamber 13 between wall members 11 and 12 and withthe core 14 positioned in the chamber and in supporting engagement withthe wall members. The air is then evacuated from the chamber and heat isapplied to the structure to bake out and remove the surface gases. Ifdesired, the chamber may be flushed out with hydrogen or a forming gassuch as a non-explosive mix ture of nitrogen and hydrogen to aid instripping surface gases, prior to the final evacuation in the Presenceof heat. In order to maintain the vacuum barrier between the core andwall members, a small amount of a gas absorbing material may be sealedwithin the chamber 13 after evacuation.

The material from which the core 14 is formed naturally must not softenor melt during heating of the structure for driving off surface gases.For effective baking out, temperatures on the order of 800 F. aredesired. The core material chosen, therefore, must not soften at thistemperature and also must possess the desired qualities of lightness andstrength. It has been found that expanded mineral materials such asporous and/or foamed ceramics or glass will afford the desiredqualities. One product particularly suited for use as a core material isa foamed glass insulating material known as and outer shells.

Foamglas and produced by the Pittsburgh Corning Corporation, 1 GatewayCenter, Pittsburgh 22, Pennsylvania. This material is formed ofinorganic glass, has a compressive strength of lbs; per square inch, adensity of 9 lbs. per cubic foot, arid will not soften at 800 F. Thethermal conductivity of the material is comparatively low, on the orderof 0.38 B.t.u./hr./sq. ft./ F./in., and therefore the material itself isa rather good heat insulator.

The passage of heat through the structure of the present invention byconduction is effectively blocked by the point contact of the core withthe rigid wall members in a substantially gas and vapor freeenvironment. Passage of heat by radiation is effectively reduced to alow value by the fact that the heat must radiate from one of the wallmembers 11 or 12 to the core 14, must then pass by conduction throughthe insulating material of the core, and then be radiated from the coreto the other of the walls.

.The heat insulated Wall structure of the present invention isparticularly adapted for the construction of containers designed tomaintain their contents at either high or low temperatures. One suchcontainer 21 is shown in Figure 1 of the drawings, this container beingespecially suited for use with articles such as packaged frozen foodsand the like. The container 21 is here of generally rectangular form andhas an insulated wall 20 which includes a rigid inner shell 22 formed todefine a storage compartment 23 for the contents to be thermallyinsulated. A rigid outer shell 24 is formed in surrounding spacedrelation to the inner shell 22 so as to define an air tight chamber 26between the inner Mounted in the chamber 26 is a rigid core 27 ofexpanding insulating material having surfaces substantially coextensivewith the inner and outer shells, these surfaces being formed with aplurality of points extending into supporting engagement with the shellsin the same manner as the points 16 of Figure 3 for supporting theshells when the chamber 26 is evacuated. Means providing an opening 28is formed through the wall 20 for access to the storage compartment 23,and the container is provided with a lid 29 which preferably alsocomprises a section of the insulated wall structure of the presentinvention. The lid 29 includes sheetlike rigid inner and outer members31 and 32 respectively which are joined at their edges, as by member 33,to provide an air tight chamber 34 in which is positioned a core 36having a plurality of points extending into supporting engagement withthe members 31 and 32 for reinforcing the structure against collapsewhen evacuated. The lid 29 is preferably formed to provide an air tightseal with the opening 28 by means of gaskets 37 which may be in the formof rubber O-rings or other similar materials such as polyethylene or thelike. The chambers 26 and 34 are evacuated by the method previouslydescribed to insulate the structure against passage of heat between thecontainer exterior and the storage compartment 23. Evacuation may beeffected through suitable tubes 38 passing through the outer shell andcommunicating with the air tight chambers, the tubes being closed offand sealed shut by any suitable means when the evacuation is complete.As an aid in evacuating, the core 27 may be formed with a series ofspaced grooves 39 in the core surfaces adjacent to the inner and outershells.

A modified form of the container of the present invention is illustratedin Figure 2 of the drawings. This container 40 is particularly adaptedto contain and thermally insulate materials in fluid form such as gases,liquids, molten metals, and powdered or granular substances. As hereshown, the fiuid container is of bottle form and includes a rigid innershell 41, defining a storage compartment 42, and a rigid outer shell 43formed in surrounding relation to the inner shell to provide an airtight chamber 44 between the shells. Mounted in the chamber 44 is a core46 similar in nature and function to the core 27 of Figure 1, andserving to reinforce the structure upon evacuation of the chamber 44.Access to the storage compartment 42 is provided by means of a tubularmember 45 joined to the inner and outer shells and affording an opening47 for the passage of fluids therethrough. Evacuation of the chamber 44may be effected through one or more tubes 48 passing through the outershell and communicating with the chamber, the tube 48 being closed offand sealed shut by any suitable means when the evacuation of the chamberhas been completed.

From the foregoing it will be apparent that the thermally insulated wallstructure and method for insulating of the present invention is readilyadaptable to a wide variety of uses and applications where a strong,light weight structure having a high resistance to heat transfer isneeded. The use of the rigid, light weight core of insulating materialto reinforce the structure, together with the highly effective means andmethod of creating a heat barrier at the points of contact of the wallmembers and core, result in a structure which can employ normally weakand frangible materials in a wall of minimum thickness and weight ascompared to its highly efficient thermal insulating ability.

While certain preferred embodiments of the present invention have beenshown and described in detail, other modifications and embodiments willbe apparent to those skilled in the art, and accordingly it is notintended to limit the invention to the exact details shown except in themanner set forth and defined in the following claims.

What is claimed is:

1. A thermally insulating wall structure comprising, in combination, apair of spaced apart parallel plates of gas impervious material,gas-tight means connecting said plates around the perimeter thereof toform a vacuum chamber therebetween, a sealable conduit communicatingwith said chamber for evacuation thereof, and a core member disposedwithin said chamber which core member is substantially co-extensivetherewith, said core member being a rigid foamed insulative materialhaving a multiplicity of minute cavities distributed throughout the bodythereof and being characterized by exterior surfaces having amultiplicity of minute concavities and intervening sharp minuteprojections which surfaces abut said plates and provide supporttherefor.

2. A thermally insulating wall structure substantially as described inclaim 1 and wherein said structure is formed into a container having anaccess opening and comprising the further combination of a removableclosure for said opening.

3. A thermally insulating wall structure substantially as described inclaim 1 wherein said structure is formed into a container and whereinthe outermost of said spaced plates is of relatively high strengthmaterial and the innermost of said spaced plates is of corrosionresistant material.

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